Conventional angular acceleration sensors may be found in Japanese Patent Laid Open Number 4-106409. FIGS. 7 and 8 show the conventional angular acceleration sensor. The conventional angular acceleration sensor has the structure as follow:
In FIG. 7, the sensor comprises four supporting posts 2, 3, 4, 5 arrayed on a base plate 1 and two fine metal lines 11, 12 connected between support posts 2, 5 and support posts 3, 4. Two support points 9, 10 formed on a metal bar 6 of a triangle are welded to the two fine metal lines 11, 12 so that the metal bar 6 is suspended at the metal lines 11, 12. The section of the metal bar 6 has a regular triangle shape. As shown in FIG. 8, a piezoelectric element 13 is adhered to the bottom of the metal bar 6 so that the piezoelectric element 13 is vibrated to Z-axis direction in response to the electrical signal applied from a voltage source Vo.
The vibration of the piezoelectric element 13 is transferred to the metal bar 6, and then it is converted into the vibrations of the A-axis and B-axis directions. When the left and right rotation forces are applied to the metal bar 6 about the center of the X-axis shown in FIG. 7, Coriolis force is generated by the rotation forces and the differences are generated between the vibration strength in the A-axis direction and the vibration strength in the B-axis direction.
The differences are converted into electrical signals through the piezoelectric elements 7, 8. The electrical signals are inputted to an amplifier A1 through resistors R1, R2. The angular acceleration is measured with the output of the amplifier A1.
In the conventional angular acceleration sensor, since it has three-dimensional structure as shown, there are difficulties in achieving a successful operation efficiency of manufacturing and a mass production. Also, since the metal bar 6 should be welded to the fine metal lines 11, 12, it requires precision work of the highest order. The angular acceleration of two-axes direction is measured by using two sensors. If two sensors are not accurately perpendicular to each other, a disturbance is occurred by each other. Also, since the Coriolis force is used in the sensor, it requires driving means, and since a power source for the driving means is needed, there has been a great difficulty in achieving a simple apparatus.
The present invention is contrived to overcome the aforementioned various problems.
It is an object of the invention to provide an angular acceleration sensor which can measure the angular acceleration by a piezoelectric element and an elastic body.
It is other object of the invention to provide an angular acceleration sensor which can measure the angular acceleration by minimizing the output to the vibration of two-axes directions.
It is another object of the invention to provide an angular acceleration sensor which can measure the angular acceleration of 2-axes directions with one sensor.
It is a further object of the invention to provide an angular acceleration sensor which can measure the angular acceleration of 2-axes directions, wherein mutual disturbance by the rotation forces in 2-axes directions can be minimized.
It is another object of the invention to provide an angular accleration sensor capable of reducing the size of the sensor.
It is an additional object of the invention to provide an angular acceleration sensor without using a Coriolis force.
In order to achieve the foregoing objects, the angular acceleration sensor of this invention comprises an elastic plate each arm of which bends towards two opposite directions by the rotation forces, a pair of piezoelectric elements adhered onto the elastic plate and each element symmetrically positioned at same distance from the center of the plate, a pair of inertia bodies symmetrically positioned at each end of the piezoelectric elements, and a support member for supporting the center of the elastic plate.